I use an ipsec-nat-t VPN (
en.wikipedia.org/wiki/IPsec#Encapsulating_Security_Payload) to get to work when I'm at home.
I
WANT this traffic to be categorized as high priority and low latency but my bandwidth demands are not high (remote desktop, VNC). As far as I can tell, my VPN traffic is categorized as "web traffic" (as is my SWTOR MMO game traffic).
It may be that DGL-5500 is already doing what I want it to but there is nothing in the GUI that tells me it is.
I haven't had a full day of working at home while someone else watches netflix so I don't much enough experience yet to evaluate how well I think my VPN traffic is being handled.
I do have the workstation that I do VPN work on prioritized highest but my understanding of the documentation is that priority is only a tie breaker for to devices with traffic that is categorized the same.